Pontine axonal injury after brain trauma and nontraumatic hypoxic-ischemicbrain damage

Experimental studies have shown that diffuse axonal injury is usually induc ed by positive or negative acceleration mechanisms. In order to determine t he reliability of axonal injury (AI) as a marker of this type of traumatic insult, we compared cases of trauma-induced focal cortical hemorrhage witho ut dural involvement (n = 67) with cases of trauma-induced subdural bleedin g without cortical hemorrhage (n = 26). Both groups exhibited a wide range of post-traumatic survival times. The injuries in the first group were caus ed mainly by direct impact to the head, those in the second by acceleration /deceleration mechanisms. The investigations were based primarily on immuno histochemical demonstration of antibodies targeted to beta-amyloid precurso r protein (beta-APP) in the pens as a marker of AI and the results were ass essed semiquantitatively. No significant differences were found between the two groups. In both groups AI was detected in 80-100% of cases with surviv al times of more than 3 h and two thirds of all positive cases showed prono unced positivity. Additional comparison of cases of brain death due to mech anical trauma (n = 14) with cases of brain death due to non-mechanical trau ma (n = Is) also disclosed no significant intergroup differences. Finally, investigations of the pens in cases of non-traumatic death due to cerebral hypoxia/ischemia (n = 51) demonstrated AI with the same frequency as in the other groups, although the expression tended to be less pronounced. Our re sults confirm that beta-APP expression in the pens is a reliable indicator of AI but does not discriminate between injuries caused by traumatic strain or shearing mechanisms and secondary damage due to cerebral hypoxia/ischem ia or edema. In the large majority of cases with prolonged post-traumatic s urvival, it can therefore be assumed that Al in the pens is the consequence of primary and/or secondary events or a combination of both, as is common in non-missile head injury survived for more than 90-120 min. Therefore, po sitive differentiation of the type of biomechanical event based on this cri terion alone is not possible.